Aluminum base alloy containing copper, cobalt, and beryllium, and method for making it



Patented Apr. 17, 1945 ALUMINUM BASE ALLOY CONTAINING COP- PER, COBALT, AND BERYLLIUM, AND METHOD FOR MAKING IT Richards H. Harrington, Schenectady, N. Y., as.- signor to General Electric Company, a corporation of New York No Drawing. Application March 28, 1942, Serial No. 436,608

8 Claims. (C1. 14811.5)

The present invention is an aluminum base alloy containing copper, cobalt and beryllium and a method for making it. In my copending application, Serial No. 436,607, I have disclosed a precipitation hardened aluminum-copper-berylliurn alloy which has unusually high tensile and elastic properties as well as a high degree of hardness. The present aluminum base alloy has improved hardness and elastic and tensile properties particularly when the cobalt and beryllium are present in the alloy in the ratio of about 6.5:1. In general, the improved alloy will contain about 2 to 6% copper, about 0.1 to 1% beryllium, 0.65 to 6.5% cobalt with the remainder aluminum.

In carrying out the present invention the melting process is substantially the same as that set forth in my copending application, Serial No. 436,607, for example a charge of aluminum is melted and raised to a temperature of about 900 C. While the melt is quietly stirred, cobalt is added to the molten aluminum either as. a solid or, preferably,' as a separately melted master alloy containing about 80% aluminum and 20 cobalt made by dissolving cobalt in molten aluminum at about 1,000 c. The melt is cooled to about 800 C. and the desired quantity of a copper-beryllium master alloy containing about 3 to 5% beryllium is added'or, if desired, a master alloy containing 12.5% beryllium and 87.5% copper may be added and the beryllium content then diluted by the addition of a desired quantity of electrolytic copper. In the melting processan excess of about 0.02%-0;05% beryllium generally is added as a deoxidizing agent but no flux is added to the melt.

The molten alloy is cooled until it just freezes in the crucible.

ite rod. y

In order to develop high physical properties in the alloys they are completely precipitation hardened, that is heated at an elevated temperature for example 520 to' 550 C. for several hour to effect a condition of solution in the alloy, quenched preferably in water, and then'aged at about 100 to 225 C.-- If copper is present in the alloy in the range of about 2.5 to 4.5 and beryllium from 0.1 to 0.75%, maximum physical properties will be developed in each alloy by maintaining the ratio of cobalt to beryllium at the critical value of 6.5 to 1.

As soonas the freezing is com-- plete the alloy. is remelted and poured in the temperature range of about 710 to 725 C. If the co- 'balt content of the alloy exceeds about 3% there may be some difficulty from segregation. To

avoid this the melt is stirred quietly with a graphple heating 4 hours'at 540 C water quenching 2' The following compositions:

3.8 Cu-0.2 lie-1.3 (Jo-94.7 Al. (CuzBezCoas l9:l:6.5)

3.5 Ou0.5 Be3.2 Co92.8 Al. (CuzBezCo as 7:l:6.5)

( show the effect on tensile properties and hardness of an increase in CoBe relative to the copper content of the alloy. In the present alloys the ratiovof copper to beryllium is not critical but the atomic Weight ratio of cobalt to beryllium (6.5: l)

is critical (with copper present preferably in a quenched from that temperatureand f-then aged, for about 8 hours at temperatures (if to,225

C. Such heat treatment develops useful properties in the alloys but the maximum properties are obtained by heating the alloys for. 4 hours at 540 v C., quenching from that-temperature, preferably in water, and then reheating for 2 toi6 hours at a temperature of 200C. With such a heat treatment alloy No. l attainsa Roclmrell B hardness of 58 to 62 while alloy No. 2 attains a Rockwell B hardness of 71 to, 75. v

The following tensile properties were obtained from sand cast A. S. T. M. standard tensile bars after applying the above preferred complete precipitation hardening heat treatment, for examto 6 hours at 200 C.!

Per cent elongation 0.2 yield strength Proportional limit Tensile strength It is clear from the above that an improvement the cobalt and beryllium in the ratio of 6.5:1.

The present alloys of aluminum, copper, cobalt and beryllium will retain superiority at elevated temperatures overstandard commercial aluminum base precipitation'hardened.alloys which are aged at temperatures in the range of about to C. Alloys Nos. 1 and 2 may be overaged at 275 C. and 300 C.-respectively'before'their hardness values fall into the hardness range for commercial aluminum base alloys which are nor mally aged at 155 to 160 C.

Natural aging consists in simply allowing the solution-quenched alloys to age at room tempera- Itockwell B hardness tures. actually efiect precipitation with the passing of time at room temperature after solution treatment while other alloys require elevated temperatures to initiate and develop precipitation. Generally with Al. alloys natural aging does not develop maximum properties, and artificial aging" (at elevated temperatures) is also required to develop stable and consistently reproducible properties for engineering applications.

Alloys within the scope of the present invention age naturally with maximum effects from a 540 C. solution treatment. As quenched, alloy No. 1 has a Rockwell B hardness of about 2'7 and at the end of 4 weeks a Rockwell B hardness of about 54. As quenched, alloy No. 2 has a Rockwell B hardness'of about 3'7 and at the end of 4 weeks a Rockwell B hardnessof about 62. If

the present aluminum base alloys containing cop. per, cobalt and beryllium are cold worked im- 'riiediately after quenching, for example preferably within 1 hour, further improvement in properties may be obtained.

treated condition particularly with respect to.

elongation. v

The maximum effect of cold working is obtained by introducing it between the solution quench and precipitation reheat. Cast rods 1" in diameter and having the composition, of alloys 1 and 2 were quenched in water after 4 hours at 540 C. Alloys Nos. 1 and 2 could be reduced 23% and 10% respectively. Further reduction causes surface cracks and internal ruptures.

After the cold reduction both alloys were aged 4 hours at 150 C. with the following results:

Ptopor 012% Tensile Per cent A My 53?; :2 strength elongation While the above-noted heat treatment is preferable, useful properties may be developed in the present alloy by precipitation agin in the temperature range of 100 to 200 C. Alloys having the specific composition indicated in the above alloys 1 and 2 do not permit sufficient cold work- Some precipitation-hardening alloys will ing and as a result the cold reduced alloys possess final elongations that ordinarily are too low for useful applications as forging alloys with the above heat treatment. If good forgeability is required the alloy content of alloys 1 and 2 preferably should not exceed 4% and the cobalt content should not be materially in excess of 1.5%.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An alloy containing 2 to 6% copper, 0.1 to

' 1% beryllium, 0.65 to 6.5% cobalt with the rev mainder substantially all aluminum. 1

2. An alloy containing 2 to 6% copper, 0.1 to 1% beryllium, 0.65 to 6.5% Cobalt with the remainder substantially all aluminum, the cobalt and beryllium being in the critical ratio of :1.

3. A precipitation hardened alloy containing 2 to 6% copper, 0.1 to 0.75% beryllium, about 0.65 to 4.8% cobalt with the remainder substantially all aluminum, the cobalt and beryllium being present in the alloy in the ratio of 65:1.

4. An alloy containing 2.5 to 4.5% copper, 0.1 to 0.75% beryllium, 0.65 to 4.8% cobalt with the remainder substantiall all aluminum, the cobalt and beryllium being present in the alloy in the ratio of 6.5:1.

5. An alloy consisting, except for normal impurities, of aluminum, copper beryllium and cobalt, each of the elements copper, beryllium and cobalt being present in the alloy in effective quantities, the total quantity of said elements being not greater than 4% of the total content of the alloy and the cobalt content of the alloy being not greater than 1.5%.

6. A precipitation hardened aluminum base al-- loy containing 2 to 6% copper, 0.1 to 1% beryllium, 0.65 to 6.5% cobalt with the remainder substantially all aluminum, the cobalt and beryllium being present in the alloy in the critical ratio of 6.5: 1.

7. The method for precipitation hardening an alloy of 3.8% copper, 0.2% beryllium, 1.3% coto 200 C.

bait, balance aluminum, which comprises heating for about 4 hours in the range of 520 to 550 C., preferably 540 C., and quenching, preferably in water, and reheating in the range of 100 C. to 250 0., preferably for 6 hours at 200 C.

8. The method for precipitation hardening an alloy containing 2 to 6% copper, 0.1 to 1% beryllium, 0.65 to 6.5% cobalt with the remainder substantially all aluminum, which comprises heating the alloy for about 4 hours at a temperature of 520 to 550 C., quenching the alloy from such temperature, cold working from 20 to 50%, and reheating it for about 2 to 6 hours in the range of RICHARDS H. HARRINGTON. 

